1. Technical Field
The present invention relates to a timing signal generating device, an electronic apparatus, a moving object, a method of generating timing signals, and a method of controlling a satellite signal receiver.
2. Related Art
GPS (Global Positioning System) as one of global navigation satellite systems (GNSS) using artificial satellites have been widely known. An extremely high precision atomic clock is mounted on a GPS satellite and transmits satellite signals on which trajectory information, accurate time information of the GPS satellite, etc. are superimposed to the ground. A GPS receiver receives the satellite signals transmitted from the GPS satellites, and performs processing of calculating a current position and a current time based on the trajectory information and the time information superimposed on the satellite signals, processing of generating accurate timing signals in which time is updated every second (1 PPS), etc.
The GPS receiver may be mounted on a moving object and used for knowing the position of the moving object, or may be installed in a location that does not move with respect to the surface of the ground (a building or the like) and used for obtaining accurate timing of 1 PSS (for example, a stock exchange or the like). In the former case, the GPS receiver is necessary to continuously perform calculation of the current position, however, in the latter case, the GPS receiver is not necessary to continuously perform calculation of the current position. Accordingly, a normal positioning mode for continuous positioning calculation and a position fix mode for outputting 1 PPS based on preset position information are generally provided in the GPS receiver.
In the normal positioning mode, satellite signals from a predetermined number (at least three for two-dimensional positioning, four for three-dimensional positioning) of GPS satellites or more are necessary for processing of solving an equation with a plurality of parameters (latitude and longitude for two-dimensional position, latitude, longitude, and altitude for three-dimensional position) for position determination and a time parameter as variables. Further, the larger the number of GPS satellites from which satellite signals can be received, the more improved the precision of positioning calculation. In contrast, in a situation in which the reception environment of satellite signals is too poor for receiving satellite signals from many GPS satellites, precision of position information of positioning results and 1 PPS is deteriorated. On the other hand, in the position fix mode, position information is preset in the GPS receiver, and 1 PPS may be generated only when satellite signals from at least one GPS satellite can be received. Therefore, in the case where the GPS receiver is installed in a location that does not move and accurate 1 PPS is necessary, use in the position fix mode is appropriate.
The precision of 1 PPS in the position fix mode depends on the precision of the set position information, and it is important to set accurate position information in the PGS receiver. As a method of acquiring accurate position information for setting in the GPS receiver, for example, a method of map reading, surveying, etc. are conceivable. However, there are problems that, in the former case, it may be difficult to acquire position information depending on the receiving location and, in the latter case, costs including expense and time may be required.
In order to solve the problems, a method of determining a position of a receiving point by performing positioning calculation using the installed GPS receiver itself and averaging position information of positioning results over a predetermined period has been proposed in Patent Document 1 (JP-A-9-178870), and position information in an arbitrary receiving location may be acquired and the cost may be reduced.
However, in the case where some error such as multipath occurs, position information as a result of positioning calculation contains a significant error. Accordingly, in the method of Patent Document 1 of averaging results of positioning calculation, an error of the position of the receiving point obtained as the averaging result may be significant. On this account, in the method of Patent Document 1, there is a problem that the precision of 1 PPS (timing signal) may be deteriorated depending on the reception environment for positioning calculation. The problem is a common problem not only for the GPS receiver but for receiving devices of other global navigation satellite systems (GLASS).